High-strength hot-rolled plated steel sheet and method for manufacturing the same

ABSTRACT

Disclosed is a high-strength hot-rolled plated steel sheet capable of suppressing material deterioration at the time of plating, while having high strength, and a method for manufacturing the same. The high-strength hot-rolled plated steel sheet may include: a hot-rolled steel sheet base material composed of 0.03-0.1 wt % of C, below 0.06 wt % of Si, 0.7-2.0 wt % of Mn, below 0.02 wt % of P, below 0.01 wt % of S, 0.1-0.5 wt % of one or more precipitate forming elements, 0.3-1.0 wt % of Al, 0.1-0.5 wt % of Mo, Fe, and unavoidable impurities; and a plated layer formed on the surface of the hot-rolled steel sheet base material.

TECHNICAL FIELD

The present invention relates to a technology for manufacturing ahot-rolled steel sheet having a plated layer formed thereon, and moreparticularly, to a high-strength hot-rolled plated steel sheet capableof suppressing material deterioration at the time of plating, whilehaving a high tensile strength of 780 Ma or more, and a method formanufacturing the same.

BACKGROUND ART

In order to overcome the age of high oil prices, the automobile industryhas tried to reduce the weight of a vehicle body. Thus, much researchhas been conducted on the development of high-strength steel forreducing the weights of parts.

Representative examples of automobile parts requiring high-strengthsteel may include a chassis. The material for a chassis requires hightensile strength for durability and high elongation and burring propertyfor implementing the shape of a complex part. In the winter season, asnow-removing work using calcium chloride is frequently conducted. Thus,the chassis may be corroded by the calcium chloride. Therefore, thematerial for a chassis requires a corrosion-resistant property in orderto prevent such corrosion.

As the material for a chassis, a plated steel sheet is usually used.Most plated steel sheets are cold-rolled plated steel sheets. Thecold-rolled plated steel sheets require a cold rolling process and ananneal heat treatment. Thus, the manufacturing process is complex, andthe manufacturing cost for the cold-rolled plated steel sheets is high.

Therefore, a hot-rolled plated steel sheet obtained by plating ahot-rolled steel sheet has been developed. In the case of a generalhot-rolled plated steel sheet, however, material deterioration may occurat the time of plating. Thus, the plating is applied only to hot-rolledsteel sheets having a tensile strength of 440 MPa or less.

The related art of the present invention is disclosed in Korean PatentLaid-open Publication No. 10-2012-0121810 published on Nov. 6, 2012 andentitled “Method of manufacturing high strength steel sheet”.

DISCLOSURE Technical Problem

Embodiments of the present invention are directed to a high-strengthhot-rolled plated steel sheet of which the material quality is notalmost changed at the time of plating, while having high strength,through process control and alloy elements such as aluminum and silicon,and a method for manufacturing the same.

Technical Solution

In an embodiment, a method for manufacturing a high-strength hot-rolledplated steel sheet may include: (a) reheating a slab composed of0.03-0.1 wt % of carbon (C), below 0.06 wt % of silicon (Si), 0.7-2.0 wt% of manganese (Mn), below 0.02 wt % of phosphorous (P), below 0.01 wt %of sulfur (S), 0.1-0.5 wt % of one or more precipitate forming elements,0.3-1.0 wt % of aluminum (Al), 0.1-0.5 wt % of molybdenum (Mo), steel(Fe), and unavoidable impurities, the precipitate forming elementsforming a precipitate at 500 to 900° C.; (b) hot-rolling the slab; (c)cooling the hot-rolled slab, and then winding the cooled slab; and (d)plating the wound slab.

The method may further include (e) alloying the slab having the platedlayer formed thereon.

The step (b) may include: roughing rolling the reheated slab at 950 to1,050° C.; and finishing rolling the roughing-rolled slab at a finishingtemperature condition of 800 to 900° C.

The step (c) may include cooling the hot-rolled slab at an averagecooling speed of 100° C./sec or more, and then winding the cooled slabat 580 to 660° C.

The step (d) may include uncoiling and pickling the wound slab, andhot-dip plating the slab without a heat treatment at a temperature ofAc1 or more.

The precipitate forming element may include one or more of 0.03-0.1 wt %of niobium (Nb), 0.03-0.1 wt % of titanium (Ti), and 0.08-0.3 wt % ofvanadium (V), or include all of Nb, Ti, and V.

In another embodiment, a high-strength hot-rolled plated steel sheet mayinclude: a hot-rolled steel sheet base material composed of 0.03-0.1 wt% of C, below 0.06 wt % of Si, 0.7-2.0 wt % of Mn, below 0.02 wt % of P,below 0.01 wt % of S, 0.1-0.5 wt % of one or more precipitate formingelements, 0.3-1.0 wt % of Al, 0.1-0.5 wt % of Mo, Fe, and unavoidableimpurities, the precipitate forming elements forming a precipitate at500 to 900° C.; and a plated layer formed on the surface of thehot-rolled steel sheet base material, wherein the high-strengthhot-rolled plated steel sheet exhibits a tensile strength of 780 to 900MPa, a yield strength of 700 to 850 MPa, an elongation of 14 to 22%, anda hole expansion of 55% or more.

The hot-rolled steel sheet base material of the hot-rolled plated steelsheet may have a microstructure which is composed of a ferritesingle-phase structure and in which fine precipitates having a size ofless than 10 nm are formed.

The precipitate forming element may include or e or more of 0.03-0.1 wt% of Nb, 0.03-0.1 wt % of Ti, and 0.08-0.3 wt % of V, or include all ofNb, Ti, and V.

Advantageous Effects

According to the embodiments of the present invention, the strength canbe secured through the precipitate forming elements such as Nb, Ti, andV, and the plateability can be improved through the suppression for Siand the addition of Al.

In particular, as 0.1-0.5 wt % of Mo is included in the hot-rolled steelsheet base material, the activity of C can be reduced at the time ofplating, and the coarsening of the precipitate can be suppressed. Thus,since material deterioration can be prevented at the time of plating, itis possible to manufacture a high-strength hot-rolled plated steel sheetwhich has an excellent elongation and burring property, while havinghigh strength.

DESCRIPTION OF DRAWINGS

The above and other aspects, features and advantages of the inventionwill become apparent from the following detailed description inconjunction with the accompanying drawings, in which:

FIG. 1 schematically shows a method for manufacturing a high-strengthhot-rolled plated steel sheet in accordance with an embodiment of thepresent invention;

FIG. 2 shows precipitates of a specimen in accordance with Embodiment 1before and after plating;

FIG. 3 shows the microstructure of the specimen in accordance withEmbodiment 1 before and after plating;

FIG. 4 shows the tensile strength and yield strength of the specimen inaccordance with Embodiment 1 before and after plating; and

FIG. 5 shows the surfaces of specimens in accordance with Embodiment 1and Comparative Examples 1 to 4.

BEST MODE

Hereafter, a high-strength hot-rolled plated steel sheet and a methodfor manufacturing the same in accordance with an embodiment of thepresent invention will be described in detail with reference to theaccompanying drawings.

High-Strength Hot-Rolled Plated Steel Sheet

The high-strength hot-rolled plated steel sheet in accordance with theembodiment of the present invention may include a hot-rolled steel sheetbase material and a plated layer formed on the surface thereof.

At this time, the hot-rolled steel sheet base material of thehigh-strength hot-rolled plated steel sheet in accordance with theembodiment of the present invention may include 0.03-0.1 wt % of carbon(C), below 0.06 wt % of silicon (Si), 0.7-2.0 wt % of manganese (Mn),below 0.02 wt % of phosphorous (P), below 0.01 wt % of sulfur (S),0.1-0.5 wt % of one or more precipitate forming elements, 0.3-1.0 wt %of aluminum (Al), and 0.1-0.5 wt % of molybdenum (Mo). The precipitateforming element may form a precipitate at a temperature of 500 to 900°C.

The other elements excluding the above-described alloy elements mayinclude steel (Fe) and unavoidable impurities which occur during asteelmaking process.

Hereafter, the roles and contents of the elements included in thehigh-strength hot-rolled plated steel sheet in accordance with theembodiment of the present invention will be described as follows.

Carbon (C)

C is an element which contributes to increasing the strength of steel.

Desirably, C may be added at 0.03-0.1 wt % with respect to the entireweight of the hot-rolled steel sheet base material in accordance withthe embodiment of the present invention. When the addition of C is lessthan 0.03 wt %, it is difficult to secure a target tensile strength of780 MPa or more. On the other hand, when the addition of C exceeds 0.1wt %, the elongation and burring property may be degraded.

Silicon (Si)

Si is an element which contributes to securing strength, and serves as adeoxidizer for removing oxygen in steel.

Desirably, Si may be added at below 0.06 wt % with respect to the entireweight of the hot-rolled steel sheet base material in accordance withthe embodiment of the present invention. When the addition of Si exceeds0.06 wt %, the plateability and alloying degree may be degraded.

Manganese (Mn)

Mn is an element which increases the strength and toughness of steel andimproves the hardenability of steel. The addition of Mn may suppress thereduction of ductility with the increase of strength, compared to theaddition of C.

Desirably, Mn may be added at 0.7-2.0 wt % with respect to the entireweight of the hot-rolled steel sheet base material in accordance withthe embodiment of the present invention. When the addition of Mn is lessthan 0.7 wt %, the addition may have no effect. On the other hand, whenthe addition of Mn exceeds 2.0 wt %, MnS-based non-metallic inclusionsmay be excessively formed. During a welding operation, a crack or thelike may occur to reduce the weldability.

Phosphorous(P)

P is an element which contributes to improving strength. However, when alarge amount is included, fine segregations as well as centersegregations may be formed to have a bad effect on the material quality,and degrade the weldability.

Thus, in the present embodiment, the content of P is limited to below0.02 wt % with respect to the entire weight of the hot-rolled steelsheet base material.

Sulfur (S)

S is an element which is coupled to Mn and forms non-metallicinclusions, and the non-metallic inclusions may degrade the toughnessand weldability.

Thus, in the present embodiment, the content of S is limited to below0.01 wt % with respect to the entire weight of the hot-rolled steelsheet base material.

Precipitate Forming Element

The precipitate forming element serves to form a precipitate at atemperature of 500 to 900° C. Representative examples of the precipitateforming element may include niobium (Nb), titanium (Ti), and vanadium(V). The hot-rolled steel sheet base material may include one or two ormore kinds of precipitate forming elements.

The precipitate forming element may be added at 0.1-0.5 wt % withrespect to the entire weight of the hot-rolled steel sheet base materialin accordance with the embodiment of the present invention. When thecontent of the precipitate forming element is less than 0.1 wt %, theeffect of strength improvement by precipitation hardening isinsufficient. On the other hand, when the content of the precipitateforming element exceeds 0.5 wt %, an excessive amount of precipitate maybe formed to degrade the processability and the surface quality.

Ti precipitate may be formed at a temperature of 900 to 1,000° C., Niprecipitate may be formed at a temperature of 600 to 800° C. and Vprecipitate may be formed at a temperature of 400 to 600° C. Consideringthis aspect, all of Ni, Ti, and V may be included in the precipitateforming element such that the precipitation is performed during a hotrolling and cooling process.

When all of Nb, Ti, and V are included in the precipitate formingelement, Nb, Ti, and V may be added at 0.03 to 0.1 wt %, 0.03-0.1%, and0.08-0.3%, respectively, which considers the following aspects. When Nband Ti are added at over 0.03 wt %, the precipitation hardening effectmay be obtained, but when Nb and Ti are added at over 0.1 wt %, theprocessability and surface quality may be degraded. Furthermore, when Vis added at over 0.08 wt %, the precipitation hardening effect may beobtained, but when V is added at over 0.3 wt %, the processability maybe degraded.

Aluminum (Al)

In the present embodiment, Al may serve as a deoxidizer, and serve toimprove the plateability.

Desirably, Al may be added at 0.3-1.0 wt % with respect to the entireweight of the hot-rolled steel sheet base material in accordance withthe embodiment of the present invention. When the addition of Al is lessthan 0.3 wt %, the deoxidation effect may be insufficient. On the otherhand, when the content of Al exceeds 1.0 wt %, the toughness of thesteel sheet may be reduced.

Molybdenum (Mo)

In the present embodiment, plating may be performed on the surface ofthe hot-rolled steel sheet, and an alloying heat treatment may beperformed, if necessary. The plating and the alloying heat treatment maybe performed at a temperature of 450 to 550° C. which overlaps theprecipitation temperature range of V. Thus, among the precipitateforming elements, V is the most suitable for precipitation hardening.However, when the V precipitate is coarsened, the material quality maybe significantly changed during the plating process or alloying heattreatment.

At this time, when Mo is added, Mo may reduce the activity of C at ahigh temperature including the temperature range of the plating andalloying heat treatment, and disturb the growth of the precipitate. As aresult, the material deterioration at the time of the plating process oralloying heat treatment can be prevented.

Desirably, Mo may be added at 0.1-0.5 wt % with respect to the entireweight of the hot-rolled steel sheet base material. When the addition ofMo is less than 0.1 wt %, the addition may have no effect. On the otherhand, when the addition of Mo exceeds 0.5 wt %, the formability andburring property of the steel sheet may be degraded.

The high-strength hot-rolled plated steel sheet in accordance with theembodiment of the present invention may be manufactured as a variety ofhot-dip plated steel sheets, through a hot-dip plating process after ahot-rolled steel sheet is manufactured from a slab. More specifically,the high-strength hot-rolled plated steel sheet may include an HGI(Hot-dip Galvanized) steel sheet having a hot-rolled galvanized layerformed thereon or an HGA (Hot-rolled Galvanized) steel sheet having analloyed hot-rolled galvanized layer formed on a hot-rolled steel sheetbase material.

The high-strength hot-rolled plated steel sheet in accordance with theembodiment of the present invention may have a final microstructurewhich is composed of a ferrite single-phase structure and in which fineprecipitates having a size of 10 nm or less are formed, through thealloy composition of Mo, Al, and the precipitate forming elements andthe hot-rolling and plating process. In the ferrite single-phasestructure, the ferrite may have an area rate of 98% or more.

Furthermore, the high-strength hot-rolled plated steel sheet inaccordance with the embodiment of the present invention may exhibit atensile strength of 780 to 900 Mpa, a yield strength of 700 to 850 MPa,an elongation of 14 to 22%, and a hole expansion rate of 55% or more.

Method for Manufacturing High-Strength Hot-Rolled Plated Steel Sheet

Hereafter, a method for manufacturing a high-strength hot-rolled platedsteel sheet in accordance with an embodiment of the present inventionwill be described.

FIG. 1 schematically shows a method for manufacturing a high-strengthhot-rolled plated steel sheet in accordance with an embodiment of thepresent invention.

Referring to FIG. 1, the method for manufacturing a high-strengthhot-rolled plated steel sheet in accordance with the embodiment of thepresent invention may include slab reheating (S110), hot rolling (S120),cooling/winding (S130), and plating (S140).

Slab Reheating

At the slab reheating step S110, a half-finished slab having theabove-described composition may be reheated. The slab reheating may beperformed at a temperature of 1,200° C. or more for 80 minutes or more,for example. Through the slab heating, the precipitate forming elementssuch as Ti, Nb, and V may be reemployed. Thus, fine precipitates may beformed during the hot rolling process.

Hot Rolling

At the hot rolling step S120, the slab may be hot-rolled.

The hot rolling may include a variety of publicly-known methods whichare performed under the condition that the finishing rolling temperatureis equal to or more than Ar3. More desirably, roughing rolling may beperformed at a temperature of 950 to 1,050° C., and finishing rollingmay be then performed at a temperature of 800 to 900° C. Under theabove-described roughing rolling condition, a large quantity of finehigh-temperature precipitates may be formed. Under the finishing rollingcondition, austenite grains before ferrite transformation may have asize of 10 to 30 μm, which is preferable in terms of strength andelongation.

Cooling/Winding

At the cooling/winding step S130, the hot-rolled slab may be cooled andwound, in order to secure sufficient strength and toughness.

At this time, the cooling may be performed at an average cooling speedof 100° C./sec or more such that grain precipitates are grown.Furthermore, the winding may be performed at a temperature of 580 to660° C. which is the most suitable for forming the ferrite single-phasestructure, and a large quality of fine precipitates may be formed due toa difference in employment rate among Ti, Nb, and V during ferritetransformation. The grain size of the ferrite structure may be set inthe range of 2 to 7 μm through the cooling/winding process.

After the winding process, the slab may be naturally cooled to the roomtemperature.

Plating

At the plating step S140, the manufactured hot-rolled steel sheet basematerial may be plated to manufacture a hot-rolled plated steel sheet.Through the plating process, the steel sheet can have corrosionresistance.

Before the plating process, a pickling process may be further performedto pickle the surface of the steel sheet using hydrochloric acid, inorder to remove scales on the hot-rolled steel sheet base material.

The plating process may include successively dipping the steel sheet ina plating bath. After the plating process, an alloying heat treatmentmay be further performed.

Before the plating process, a heat treatment may be performed to heatthe steel sheet at a temperature of Ac1 or more. However, since thesteel sheet in accordance with the embodiment of the present inventionhas a small difference in material quality between before and after theplating process, hot-dip plating may be performed without a heattreatment after the pickling process. When a heat treatment is skipped,the manufacturing cost for the hot-rolled plated steel sheet can besignificantly reduced.

Through the plating process, an HGI or HGA steel sheet may bemanufactured.

The plating process may be performed at a temperature of 450 to 500° C.Furthermore, the alloying heat treatment may be performed at atemperature of 460 to 500° C. for about 5 to 100 seconds.

Embodiments

Hereafter, the structure and operation of the present invention will bedescribed in more detail with reference to preferred embodiments.However, the embodiments are only examples, and cannot limit the scopeof the present invention.

Since contents which are not described herein can be easily understoodby those skilled in the art, the descriptions thereof are omittedherein.

1. Manufacturing Specimens of Hot-Rolled Plated Steel Sheet

Ingots having compositions of Table 1 below were manufactured, and thenreheated at a temperature of 1,250° C. for 120 minutes. Then, roughingrolling was performed at a temperature of about 1,000° C., and finishingrolling was performed at a temperature of 850° C. Then, the ingots werecooled to 600° C. at an average cooling speed of 150° C./sec, andmaintained at 600° C. for 30 seconds. Then, the ingots were naturallycooled to manufacture specimens of the hot-rolled steel sheet basematerial.

Then, the specimens of the hot-rolled steel sheet base material werepickled, hot-dip galvanized at a temperature of 460° C., andalloying-heat-treated at a temperature of 500° C.

TABLE 1 (Unit: wt %) C Si Mn P S Nb Ti V Al Mo Embodiments 1 0.05 0.0051.7 0.02 0.003 0.07 0.06 0.09 0.3 0.3 2 0.08 0.01 1.2 0.01 0.005 0.05 —0.20 0.4 0.3 3 0.04 0.02 1.5 0.01 0.005 — 0.08 0.15 0.5 0.4 Comparative1 0.05 0.005 1.8 0.02 0.003 0.01 0.01 0.01 0.4 0.3 examples 2 0.05 0.031.5 0.01 0.005 0.05 0.04 0.08 0.5 — 3 0.05 0.15 1.5 0.01 0.01 0.07 0.060.09 0.3 0.3 4 0.05 0.30 1.7 0.02 0.003 0.07 0.06 0.09 0.3 0.3 5 0.050.40 1.7 0.02 0.003 0.07 0.06 0.09 0.3 0.3 6 0.05 0.50 1.7 0.02 0.0030.07 0.06 0.09 0.3 0.3

2. Microstructure

FIG. 2 shows precipitates of the specimen in accordance with Embodiment1 before and after plating. Referring to FIG. 2, the size ofprecipitates in the specimen in accordance with Embodiment 1 is notchanged before and after plating.

FIG. 3 shows the microstructure of the specimen in accordance withEmbodiment 1 before and after plating. Referring to FIG. 3, the specimenin accordance with Embodiment 1 has a ferrite single-phase structurebefore and after plating, and the structure thereof is not changed.

The results of FIGS. 2 and 3 are because, as the activity of C wasreduced due to the addition of Mo, material deterioration did not occurat the time of plating.

3. Mechanical Property Evaluation

For the specimens in accordance with Embodiments 1 to 3 and ComparativeExamples 1 to 7, a tensile test and a burring property (hole expansion)test were performed. After an alloying heat treatment, the surfaces ofthe specimens were observed.

The tensile test was performed by a JIS-5 specimen.

The hole expansion test was performed as follows: a hole having theinitial diameter d₀ of 10 mm was formed and then expanded by a 60-degreecone punch, and the diameter d of the hole at the point of time that acrack passed through the sheet was measured to evaluate the holeexpansion ((d-d₀)/d₀×100).

TABLE 2 Tensile Yield strength strength Elongation Hole (MPa) (MPa) (%)Expansion (%) Embodiments 1 840 800 22 65 2 828 792 22 66 3 853 816 2161 Comparative 1 736 624 24 68 Examples 2 772 714 23 64 3 844 801 21 644 867 816 19 62 5 868 821 18 62 6 871 822 16 61

Referring to Table 2, the specimens in accordance with Embodiments 1 to3, which satisfy the conditions suggested in the present invention,satisfy a tensile strength of 780 to 900 MPa, a yield strength of 700 to850 MPa, an elongation of 14 to 22%, and a hole expansion of 55% ormore, which correspond to the target values of the tensile strength, theyield strength, the elongation, and the hole expansion.

On the other hand, the specimen in accordance with Comparative Example1, which does not include a sufficient amount of precipitate formingelement, exhibits low strength, and the specimen in accordance withComparative Example 2, which does not include Mo, also exhibits lowstrength. The results of Comparative Examples 1 and 2 are because noprecipitates were formed due to an insufficient amount of precipitateforming element, or precipitates were coarsened during a plating processor a maintenance process after a cooling process, which corresponds to awinding process.

Furthermore, the specimens in accordance with Comparative Examples 3 to6, which include an excessive amount of Si, have mechanical propertieswhich satisfy the target values.

As illustrated in FIG. 5, however, when an excessive amount of Si isadded, the plated layers of the specimens are not uniform, and thesurface states of the specimens are not satisfactory.

Although some embodiments have been provided to illustrate the inventionin conjunction with the drawings, it will be apparent to those skilledin the art that the embodiments are given by way of illustration only,and that various modifications and equivalent embodiments can be madewithout departing from the spirit and scope of the invention. The scopeof the invention should be limited only by the accompanying claims.

1. A method for manufacturing a high-strength hot-rolled plated steelsheet, comprising: (a) reheating a slab composed of 0.03-0.1 wt % ofcarbon (C), below 0.06 wt % of silicon (Si), 0.7-2.0 wt % of manganese(Mn), below 0.02 wt % of phosphorous (P), below 0.01 wt % of sulfur (S),0.1-0.5 wt % of one or more precipitate forming elements, 0.3-1.0 wt %of aluminum (Al), 0.1-0.5 wt % of molybdenum (Mo), steel (Fe), andunavoidable impurities, the precipitate forming elements forming aprecipitate at 500 to 900° C; (b) hot-rolling the slab; (c) cooling thehot-rolled slab, and then winding the cooled slab; and (d) plating thewound slab.
 2. The method of claim 1, further comprising the step ofalloying the slab having the plated layer formed thereon.
 3. The methodof claim 1, wherein the step of hot rolling the slab comprises: roughingrolling the reheated slab at 950 to 1,050° C.; and finishing rolling theroughing-rolled slab at a finishing temperature condition of 800 to 900°C.
 4. The method of claim 1, wherein the step of cooling the hot-rolledslab, and the winding the cooled slab comprises cooling the hot-rolledslab at an average cooling speed of 100° C./sec or more, and thenwinding the cooled slab at 580 to 660° C.
 5. The method of claim 1,wherein the step of plating the wound slab comprises uncoiling andpickling the wound slab, and hot-dip plating the slab without a heattreatment at a temperature of Ac1 or more.
 6. The method of claim 1,wherein the precipitate forming element comprises at least one of0.03-0.1 wt % of niobium (Nb), 0.03-0.1 wt % of titanium (Ti), and0.08-0.3 wt % of vanadium (V).
 7. The method of claim 1, wherein theprecipitate forming element comprises 0.03-0.1 wt % of Nb, 0.03-0.1 wt %of Ti, and 0.08-0.3 wt % of V.
 8. A high-strength hot-rolled platedsteel sheet comprising: a hot-rolled steel sheet base material composedof 0.03-0.1 wt % of C, below 0.06 wt % of Si, 0.7-2.0 wt % of Mn, below0.02 wt % of P, below 0.01 wt % of S, 0.1-0.5 wt % of one or moreprecipitate forming elements, 0.3-1.0 wt % of Al, 0.1-0.5 wt % of Mo,Fe, and unavoidable impurities, the precipitate forming elements forminga precipitate at 500 to 900° C.; and a plated layer formed on thesurface of the hot-rolled steel sheet base material, wherein thehigh-strength hot-rolled plated steel sheet exhibits a tensile strengthof 780 to 900 MPa, a yield strength of 700 to 850 MPa, an elongation of14 to 22%, and a hole expansion of 55% or more.
 9. The high-strengthhot-rolled plated steel sheet of claim 8, wherein the hot-rolled steelsheet base material of the hot-rolled plated steel sheet has amicrostructure which is composed of a ferrite single-phase structure andin which fine precipitates having a size of less than 10 nm are formed.10. The high-strength hot-rolled plated steel sheet of claim 8, whereinthe precipitate forming element comprises at least one of 0.03-0.1 wt %of Nb, 0.03-0.1 wt % of Ti, and 0.08-0.3 wt % of V.
 11. Thehigh-strength hot-rolled plated steel sheet of claim 8, wherein theprecipitate forming element comprises 0.03-0.1 wt % of Nb, 0.03-0.1 wt %of Ti, and 0.08-0.3 wt % of V.